create fail pass flag

choice.go

@@ -230,7 +230,8 @@ func (p *choiceParser) parse(c *context) {
 		c.failingParser = failingParser
 		if c.failingParser == nil &&
 			p.commitType()&userDefined != 0 &&
-			p.commitType()&Whitespace == 0 {
+			p.commitType()&Whitespace == 0 &&
+			p.commitType()&FailPass == 0 {
 			c.failingParser = p
 		}
 	}

context.go

@@ -2,6 +2,7 @@ package treerack
 
 import (
 	"io"
+	"strings"
 	"unicode"
 )
 
@@ -128,6 +129,11 @@ func findLine(tokens []rune, offset int) (line, column int) {
 
 func (c *context) parseError(p parser) error {
 	definition := p.nodeName()
+	flagIndex := strings.Index(definition, ":")
+	if flagIndex > 0 {
+		definition = definition[:flagIndex]
+	}
+
 	if c.failingParser == nil {
 		c.failOffset = c.consumed
 	}

define.go

@@ -20,6 +20,8 @@ func flagsToCommitType(n []*Node) CommitType {
 			ct |= Whitespace
 		case "nows":
 			ct |= NoWhitespace
+		case "failpass":
+			ct |= FailPass
 		case "root":
 			ct |= Root
 		}

errors_test.go

@@ -305,9 +305,34 @@ func TestLongestFail(t *testing.T) {
 		doc:root                = (expression (statement-separator+ expression)*)?
 	`
 
+	const doc = `f(a b c)`
+
 	testParseError(t, syntax, []errorTestItem{{
-		title: "choice",
-		doc:   "f(a b c)",
+		title: "fail on longest failing parser",
+		doc:   doc,
+		perr: ParseError{
+			Offset:     4,
+			Line:       0,
+			Column:     4,
+			Definition: "function-application",
+		},
+	}})
+}
+
+func TestFailPass(t *testing.T) {
+	const syntax = `
+		space:ws                = " ";
+		symbol:nows             = [a-z]+;
+		list-separator:failpass = ",";
+		argument-list:failpass  = (symbol (list-separator+ symbol)*);
+		function-application    = symbol "(" argument-list? ")";
+	`
+
+	const doc = `f(a b c)`
+
+	testParseError(t, syntax, []errorTestItem{{
+		title: "fail in outer definition",
+		doc:   doc,
 		perr: ParseError{
 			Offset:     4,
 			Line:       0,

sequence.go

@@ -314,7 +314,8 @@ func (p *sequenceParser) parse(c *context) {
 			if currentCount < p.ranges[itemIndex][0] {
 				if c.failingParser == nil &&
 					p.commitType()&userDefined != 0 &&
-					p.commitType()&Whitespace == 0 {
+					p.commitType()&Whitespace == 0 &&
+					p.commitType()&FailPass == 0 {
 					c.failingParser = p
 				}